Primary adenocarcinoma of the vermiform appendix is a rare clinical entity that is virtually never diagnosed preoperatively. A case of mucin-producing adenocarcinoma of the appendix manifesting as a pelvic mass is presented. The ultrasonographic finding of a multilocular cystic lesion with thick septa and solid components was consistent with an ovarian cystadenocarcinoma. A review of primary appendiceal neoplasms with ovarian metastases is given.